Journal of Advanced Research in Materials Science 36, Issue 1 (2017) 21-27

21

Journal of Advanced Research in

Materials Science

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ISSN: 2289-7992

A description on deformation and failure of hybrid composite

under static loading

Ahmad Fuad Ab Ghani1,2,∗, Jamaluddin Mahmud2

1 Fakulti Teknologi Kejuruteraan, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia 2 Fakulti Kejuruteraan Mekanikal, Menara 1, Kompleks Kejuruteraan, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia

ARTICLE INFO ABSTRACT

Article history:

Received 6 July 2017

Received in revised form 28 August 2017

Accepted 25 September 2017

Available online 8 October 2017

A description on deformation and failure study of hybrid composite under static

loading is given. Numerous advantages in terms of mechanical properties obtained by

using hybrid composite are observed from literatures and expected from this research

project. Lacks of experimental techniques and finite element modeling (FEM) at micro

and macro level have limits the findings and explanation on mechanics and material

science of hybrid composite under static loading. The use of Scanning Electron

Microscope (SEM) is proposed to view precisely the microstructure behavior pre and

after loading. Hybrid composite will be formed by unidirectional prepreg Carbon fiber

reinforced polymer (CFRP) and Glass fiber reinforced polymer (GFRP) cured under high

temperature and high pressure. Micro hardness test is proposed as a measure of

hardness between different arrangements of hybrid composite. The framework of

relation between elasticity, tensile characterization, shear properties, microstructure

study and hardness test of hybrid composite is formulated for this research project.

Keywords:

Hybrid Composite; Tensile Properties;

Shear Properties Static Loading; Micro

hardness Copyright © 2017 PENERBIT AKADEMIA BARU - All rights reserved

1. Introduction

Hybrid composite is formed by reinforcement of two or more types of fiber bound with matrix. It

is an improved composite in terms of mechanical properties as compared to conventional Fiber

Reinforced Polymer (FRP) composite such as Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber

Reinforced Polymer (GFRP). Hybrids composite normally have more than one reinforcing sections or

multiple reinforcing and multiple matrix section or single reinforcing phase with multiple matrix

phases. The deformation and stress analysis of hybrid composites is a result of compromise between

individual components forming the hybrid composite, where each constituent has its own

advantages and disadvantages with respect to mechanical properties [1]. The study of mechanical

properties of hybrid composite with induce and yield results that could be of parameters for

composite designers, engineers and practitioners to opt for hybrid composite for their structural

∗ Corresponding author.

E-mail address: ahmadfuad@utem.edu.my (Ahmad Fuad Ab Ghani)

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parts or components. There is still a lack of research and development in terms of findings from

hybrid composite and its relation in terms of material properties and mechanical behavior especially

for promising composite Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer

(GFRP) which used widely in aerospace, marine, infrastructure industry [2].

2. Tensile Properties of Hybrid Composite

Tensile properties are of critical parameters differentiating stiff and strong materials from tensile

perspective either static or dynamic loading and uniaxial loading or multiaxial loading. It is interesting

and of researchers’ as well as industrial practitioners’ inquiry as how does it behaves under tensile

loading as compared to conventional composite (single type of fiber). Is it worth the cost saving from

monetary point of view with respect to tensile properties such as tensile modulus in

longitudinal/transverse direction, tensile strength in longitudinal/transverse direction, failure strain

in longitudinal/transverse direction which are more important. Hybrid composite consists of more

than one type of fiber where the advantages of one type of fiber in terms of mechanical properties

could assist with the other. The mechanical properties of a hybrid composite depend on its fiber

content, orientation, dimension of constituent fibers (diameter), level of intermixing of fibers,

interface bonding between fiber and matrix and fibers arrangement between different type of fibers.

The strength of hybrid composite also depends on the failure strain of each fibers where higher

failure strain on a type of fiber could complement the other [2]. The mechanical properties of hybrid

composite such as modulus of elasticity and improved tensile strength which lead to the beneficial

on applications in aerospace, automotive, marine etc. Tensile properties of hybrid composite are able

to surpass the properties of single composite but it was found that interfacial interaction between

the fiber and matrix was relatively weak based on SEM image of the fractured surface [3]. It was

observed that the measured tensile strength of the hybrid composite lies in between that of the solid

CFRP and solid GFRP. This means that the mechanical properties of GFRP are improved on the

modulus of elasticity and the tensile strength [4].

3. Shear Properties of Hybrid Composite

In real engineering scenario, part or structural component will be subjected to multiaxial loading

that includes shear loading. It is complex in terms of shear field obtained for conventional

unidirectional composite and it is even more difficult for hybrid composite shear stress and strain

computation due to nature of loading as well as fiber orientation in hybrid composite. Different

techniques performed by scholars to measure the shear strength of unidirectional carbon fiber

composites. The results of the shear modulus can be predicted with sufficient accuracy via

experimental method using off axis shear stress testing and Iosipescu shear test method which able

to produce perfect shear field on v notch region to determine shear strength as well [5]. The

computation of the shear modulus and the shear strength of composite material using Iosipescu V

Notch Shear Test is suitable due to perfect shear field generated. Literature shows that the Iosipescu

V Notch shear test with a modified Wyoming test fixture (ATSM D5379) was performed

experimentally and compared theoretically to determine the in plane shear modulus and strength of

unidirectional hybrid composites [6].In this research project, both off axis shear test and Iosipescu V

Notch shear test will be employed to study the deformation and strength behaviour of hybrid

composite at different layup and arrangement between carbon fiber and glass fiber material.

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4. Microstructure Study of Hybrid Composite

In order to understand the structure and failure mode of hybrid composite as compared to

each single constituent of composite, microstructure study of preloading and after loading on

hybrid composite is proposed. Failure will happen based on many modes such as cracking

between fiber and matrix when subjected to load (e.g. tensile, compression, shear). The study of

microstructure on hybrid composite material is essential in understanding the causes of failures

and failure modes. Another research observed that during service life, composite structures will

experience high stresses resulting in crack propagation through fiber matrix interfaces [7]. Reason

of forming hybrid composite is to enhance each constituent’s composite strength, toughness, as

well as its reliability towards failure. The area where CFRP and GFRP composite placed together

in hybrid composite is the interface region. Most of hybrid composite failures are reportedly

occurring at this interface region. Another interesting study observed that weak point in hybrid

composite materials lies on the interface area [8]. Figure 1 shows the cross sectional view of CFRP

unidirectional prepreg after curing, as observed using SEM at 500 times magnification at 50µm.

The diameter of CFRP as observed is around 6.7µm to 7.5 µm observed at 5000 times

magnification.

Fig. 1. CFRP unidirectional SEM cross sectional view

Fig.2. Interlayer cracking in unidirectional kevlar

hybrid composite [9]

Fig.3. Microstructural longitudinal view of

unidirectional CFRP using SEM

Macroscopic view is a view that can be observed by the eye. An example of macroscopic view of

composite failure is when human can see the composite cracking or ruptured of composite.

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Microscopic view is a view that cannot be observed by naked eye and in need of asssitance for image

magnification. An article [1] on hybrid composite microstructural study observed the failure mode of

the hybrid composite by analyzing the morphology using Scanning Electron Microscope (SEM). They

analyzed the cross sectional observation of untested samples which focussing on the fibre/matrix

interface and matrix’s void contents. The interstitial regions which serve as crack initiators are

observed in woven and UD samples [9]. Meanwhile, Figure 2 shows the cracking observed in UD

kevlar sample [9]. Interlayer delamination and interlayer cracking are two most common failure

modes. Fiber pull-out is another failure mode occurs in CFRP and GFRP. Figure 3 depicts longitudinal

view of unidirectional CFRP using SEM at 500 times magnification performed at material science lab

in Fakulti Kejuruteraan Mekanikal, Universiti Teknikal Malaysia, Melaka. It depicts the layup

longitudinal view of composite material that opens to the possibility of visualizing the fiber

deformation, failure mode, characteristic of hybrid composite which is the research interest under

study.

5. Hardness Study of Hybrid Composite

The research also encompasses the study of hardness of hybrid composite and its relation to

tensile strength and possibly other mechanical properties. Hardness is defined as resistance of a

material to localized deformation. The deformation can happen due to indentation mode, bending

or cutting [10]. Hybrid composite is expected to have better flexibility due to the combined fiber

reinforced composites as compared to the flexibility of each constituent of the composite. For

instance CFRP/GFRP hybrid composite consists of high modulus of elasticity fiber in CFRP and low

modulus of elasticity fiber in GFRP. The higher modulus of elasticity fiber offers stiffness and load

holding capability while the low elasticity fiber makes the hybrid composite more resilient and more

cost effective. Relation of hardness to other properties of composite such as strength in longitudinal

and transverse direction has not been studied widely by researchers. This makes research in this area

promising and has served as part of the motivation for this project to be conducted. During micro

hardness test experiment, the indentations are minimal and computed using a microscope. Hardness

of different micro constituents can be measured together with hardness gradients as experienced in

the case of hardening behavior [11].Conversions from micro hardness values to tensile strength and

other hardness scales such as HB, HR etc. are available for many metals and alloys but not for

composite material. It is a challenge for this proposed research project to explore the possible

relation in regards to hardness and tensile deformation behavior of hybrid composite.

5.1 Hardness Test on Hybrid Composite

A research discussed on the hardness of specimens tested using micro hardness Vickers test and

the hardness was computed at three different locations of the specimen where the average value

was taken [12]. Several researches tested specimen using Barcol hardness test. It was measured using

a HPE Bareiss Durometer based on ASTM D2583 and produced an average out of 20 measurements

[13]. They concluded that carbon fiber reinforced epoxy (CFRP) experienced higher tensile strength

than GFRP and Hybrid composite (GFRP + CFRP) as shown in Figure 4. They also found that tensile

strength increased when the hardness increased proportionately [12]. Micro hardness value also

increases proportionately with incremental amount of carbon fiber content as per Figure 5.

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5.2 Relation of Hardness and Tensile Strength

It is of interest to study and synthesize the relation of one material properties to another. It

perhaps could bring to significant findings for better performance prediction and optimization.

Hardness encompasses other mechanical properties such as the resistance to friction and abrasion

that occur at micro scale in hybrid composite material [13]. The phenomenon associates hardness

with tensile strength and resistance to deformation is relying on the modulus of elasticity level [14].

Fig.4. The effect of reinforcements on

UTS of the fibers reinforced composite [12]

Fig.5. The effect of reinforcement on micro

hardness of the fibers reinforced composites

[12]

Fig. 6. The Framework on Hybrid Composite Deformation and Failure Study

Research shows that estimation of yield strength in tension is approximately 1/3 of the material

hardness [10]. An approximate relationship between the hardness and the tensile strength of steel

for instance is,

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TS (MPa) = 3.55 X HB [HB equal or less than 175] (1)

= 3.38 X HB [HB more than 175] (2)

where HB is the Brinnell Hardness of the material measured with a standard indenter using 3000 kgf

load [10]. Figure 6 shows the framework of studying deformation and failure characterization of

hybrid composite via experimental and finite element method. Tensile strength is associated with

many factors during tensile, shear and fatigue loading such as matrix cracking, fretting, fiber bridging,

delamination etc. Problem of matrix cracking in composite has been reviewed under fatigue loading,

tensile loading, and flexural loading condition by several scholars [15, 16]. The introduction

combination of low modulus and high modulus of hybrid composite constituents will brings to

advantage of degrading of load transfer between matrices and fibre [17].

6. Conclusion

The rationale for studying the characteristic of hybrid composite is discussed. Methodology of

tensile test, shear test, microstructure test and micro hardness test are elaborated in terms of

principle and application on hybrid composite. The relation between different compositions of hybrid

composite was studied from tensile properties perspective, shear properties characterization and

microstructure field. Micro hardness findings are expected to contribute significantly in terms of its

relation with other mechanical properties of hybrid composite such as tensile strength obtained from

experimental campaigns. The proposed research project is suggested for experimentally and

supported by findings to be obtained from Finite Element Modelling which are not discussed in this

paper.

ACKNOWLEDGEMENT

Author would like to thank Fakulti Kejuruteraan Mekanikal (FKM), Universiti Teknikal Malaysia

Melaka (UTeM) for the equipment and professional technical support during test at material science

lab for this research project.

References

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